Catalyst recovery from alcohol synthesis process



June 19, 1956 J. K. MERTZW El LLER CATALYST RECOVERY FROM ALCOHOL SYNTHESIS PROCESS Filed Dec. 5l, 1952 Dmmwmums Joseph Kmert'zzeler Gavenbor ma w O e United States Patent O CATALYST RECOVERY FROM ALCOHOL SYNTHESIS PROCESS Joseph K. Mertzweller, Baton Rouge, La., assigner to Esso Research and Engineering Company, a corporation of Delaware Application December 31, 1952, Serial No. 328,951

9 Claims. (Cl. 260=414) The present invention relates to the preparation of organic compounds by the reaction of carbon monoxide and hydrogen with carbon compounds containing olenic linkages in the presence of carbonylation catalyst. More specifically, the present invention relates to the recovery of the cobalt catalyst utilized in the foregoing reaction from the product of the first stage of cobalt carbonylation reaction for further use in the process. The present application is a continuation-in-part of Serial No. 270,837, filed February 9, 1952.

It is now well known in the art that oxygenated organic compounds may be synthesized from organic compounds containing olefinic linkages by a reaction with carbon monoxide and hydrogen in the presence of a catalyst containing metals of the iron group, such as cobalt or iron, preferably the former, in an essentially three-stage process. In the first stage, the olefinic material, catalyst and the proper proportions of CO and H2 are reacted to give a product consisting predominantly of aldehydes containing one more carbon atom than the reacted olefin. This oxygenated organic mixture, which contains dissolved in it salts and the carbonyls and molecular complexes of the metal catalyst, is treated in a second stage to cause removal of soluble metal compounds from the organic material in a catalyst removal zone. The catalyst-free material is then generally hydrogenated to the corresponding alcohols, or may be oxidized to the corresponding acid.

This carbonylation reaction provides a particularly attractive method for preparing valuable primary alcohols which find large markets, particularly as intermediates for plasticizers, detergents and solvents. Amenable to the reaction are long and short chained olefinic compounds, depending upon the type alcohols desired. l' Not only olens, but most organic compounds possessing at least one non-aromatic carbon-carbon double bond may be reacted by this method. Thus, straight and branch-chained olefins and diolefins such as propylene, butylene, pentene, hexene, heptene, butadiene, pentadiene, styrene, olefin polymers such as diand tri-isobutylene and hexene and heptene dimers, polypropylene, olelinic fractions from the hydrocarbon synthesis process, thermal or catalytic cracking operations, and other sources of hydrocarbon fractions containing olefins may be used as starting material, depending upon the nature of the final product desired.

The catalyst in the lirst stage of the prior art processes is usually added in the form of salts of the catalytically active metal withl high molecular fatty acids, such as stearic, oleic, palmitic, naphthenic, etc., acids. Thus, suitable catalysts are, for example, cobalt oleate or naphthenate. These salts are soluble in the liquid olefin feed and may be supplied to the first stage as hydrocarbon solution or dissolved in the olefin feed.

The synthesis gas mixture fed to the rst stage may consist of any ratio Aof H2 to CO, but preferably these gases are present in about equal volumes. The conditions for reacting oletins with H2 and CO vary somewhat in accordance Ywith the nature of the olefin feed, but the reaction is generally conducted at pressures in the range ICC of about 1500 to 4500 p. s. i. g. and at temperatures in the range of about 150-450 F. The ratio of synthesis gas to olefin feed may vary widely; in general about 2500 to 15,000 cubic feet of H2|-CO per barrel of olefin feed are employed.

At the end of the first stage, when the desired conversion of olefins to oxygenated compounds has been effected, the product and the unreacted material are generaliy withdrawn to a catalyst removal zone, where dissolved catalyst is removed from the mixture and it is to this stage that the present principal invention applies.

From the catalyst removal zone the reaction products, comprising essentially aldehydes, may be transferred to a hydrogenation zone, and the products reduced to the corresponding alcohols in a manner known per se.

One of the problems involved in the aldehyde synthesis reaction is the fact that the catalyst metal, such as cobalt, though added as an organic salt, reacts with carbon monoxide under the synthesis conditions to form the metal carbonyl. There is basis for the belief that the metal carbonyl itself is the active form of the catalyst. This dissolved catalyst must be removed prior to the subsequent hydrogenation, as otherwise it would separate out on the hydrogenation catalyst, plug transfer lines and heat exchangers, etc. The carbonyl remains dissolved in the reaction product from the primary carbonylation stage and is therefore removed in the catalyst removal, or decobalting zone. A way to remove the cobalt is by a thermal method wherein the aldehyde product containing the dissolved cobalt is heated to a temperature of from 300-400o F. preferably in the presence of an inert gas, a steam coil being immersed in the liquid. This process has the marked disadvantage in that not only is decobalting incomplete, because aldehyde-soluble cobalt compounds that are not carbonyls are not decomposed by this method, but also the cobalt metal that results from the thermal decomposition deposits as hard crusts on the heat transfer surfaces, and is difficult to remove and recover, and frequent shut down and turnarounds are necessary.

These diiculties were to a great extent removed, and a long step forward taken. when it was found that when the cobalt-contaminated aldehyde product comprising the first stage reactor efliuent was treated with dilute aqueous solutions of organic acids whose cobalt salts are water soluble and oil-insoluble, exceptionally efficient decobalting was obtained with residual cobalt content of the aldehyde product less than ten parts per million. The thermal decobalting process frequently left a feed for the subsequent hydrogenation process containing from -500 parts per million of dissolved cobalt. This resulted from the fact, as indicated above, that although the cobalt carbonyls are readily decomposed at the thermal conditions, the other oil-soluble compounds of cobalt found in the aldehyde product, such as cobalt soaps and salts orginating from secondary reactions in the aldehyde synthesis stage, are quite stable at these temperatures.

An important advantage of said decobalting, besides the fact that lower temperatures are required than in thermal decobalting, is that cobalt recovery is considerably simplified and made more nearly quantitative. Because of the strategic importance of this metal, it is essential for an economically feasible process that substantially all the metal be recovered and reutilized. Thus, instead of precipitating the metal as a solid on packing tubes, reactor walls or heat transfer surfaces, as in prior art practices, the effect of dilute aqueous organic acid injection is to convert substantially all the cobalt dissolved in the aldehyde product, regardless of what form it is present, into a water-soluble salt, and `this aqueous stream is readily separated from the decobalted aldehyde product.

The utilization of this aqueous cobalt stream, however which may have a cobalt concentration of from 0.1 to 10%, poses several real problems. The most obvious and direct method of utilization consists of recycling directly the aqueous stream to the aldehyde synthesis reactor. This step, however, may be quite undesirable in that it introduces considerable quantities of water into the reactor oven, and results in iiooding and quenching of the reaction. Under certain circumstances, a limited amount of water in the primary reactor may be benecial, but under other circumstances, particularly when the cobalt concentration of the recovered aqueous stream is dilute, i, e., about 0.1 to 3% cobalt, flooding is very likely to occur if it is attempted to recycle enough to provide adequate catalyst concentration in the reactor oven corresponding to 0.1 to 0.5% cobalt on olen. Furthermore, the addition of water is conducive to secondary reaction product formation, particularly fatty acids instead of the desired aldehydes.

As an alternate process, the aqueous cobalt solution may be converted, prior to recycling to the reaction, into an oil-soluble cobalt form similar to the form in which it is initially introduced, i. e., the oil-soluble, high molecular weight fatty acid salt of cobalt, such as cobalt oleate, naphthenate, and the like. This avoids the necessity of recycling large amounts of water. However, when it was attempted to convert the water-soluble cobalt salt, which was assumed to be cobalt acetate (when acetic acid is the decobalting agent) into the corresponding cobalt oleate by heating in the presence of oleic acid and sodium hydroxide, a surprising result was obtained. It was found that only a portion of the cobalt in the aqueous solution was converted into cobalt oleate, in accordance with the reaction.

On analysis of the reaction products, after the cobalt oleate formed above had been removed, it was found that a substantial portion of cobalt was still in the water layer.

lt is evident, therefore, that a significant portion of the cobalt present in the water solution resulting from acid decobalting is not in a form available for reaction with an organic acid or an alkali, and hence cannot be converted by conventional processes into oil-soluble cobalt soaps.

it is, therefore, an object of this invention to provide an improved means for removing and recovering cobalt catalyst from conversion products resulting from the reaction of oleiins, CO and Hz, and efficiently reutilizing the recovered catalyst in the reaction.

lt is also a purpose of the invention to set forth a process of converting substantially completely the water-soluble cobalt recovered from a dilute acid decobalting process into an oil-soluble salt, and recycling the latter to the aldehyde synthesis reaction zone.

Other and further purposes, objects, and advantages of the present invention will become apparent from the more detailed description hereafter.

The surprising fact has now been found that the acid treatment of the aldehyde does not convert the cobalt carbonyl dissolved therein completely, or even substantially, into cobalt acetate under the reaction conditions, which comprise temperatures n higher than 200 F. to prevent decomposition of the carbonyl into metallic cobalt. Instead of the expected hydrolytic reaction of cobalt carbonyl and other cobalt compounds with the hot dilute acetic acid to form cobalt acetate, it has now been discovered that a substantial proportion of the cobalt in the water layer is present as the anion rather than as the cobaltous cation Careful analysis of the Water layer has now shown that 3050% of the total cobalt is present as cobalt anion Co(CO)4-, and the corresponding cobalt salt, Co(Co(CO)4)2. From this it is readily seen that when this aqueous solution is treated with oleic acid and caustic to convert the cobalt acetate to cobalt oleate, the cobalt in the form of the anion Co(CO)4 is not available for conversion to the fatty acid salt. It is probable that the cobalt salt, Co(Co(CO)4)2, is formed by extraction of aldehyde containing free cobalt hydrocarbonyl, HCo(CO)4, with aqueous solution of cobalt acetate initially formed.

One method which has been suggested to overcome this problemi consists in making the aqueous solution from acid decobalting strongly alkaline, oxidizing the salt lla(Co(CQ)4-), followed by acidification.

rl`hus it has been found that when these aqueous solutions of cobalt wherein that element is present as part of the anion CMCOM" are treated with an oxidizing agent, such as air, in an alkaline medium, the cobalt present originally as the anion is converted to insoluble compounds, which upon acidification of the solution is converted to the cobaltous ion. ln addition the cobaltous ion (Co++) originally present in the solution is precipitated as cobaltous hydroxide, the cobaltous hydroxide then being reconverted to cobaltous ion in the subsequent acidification. The overall effect is to convert the major portion of the cobalt originally present in the aqueous decobalter solution, i. e. Co+r and Co(CO)4-, to the cobaltous ion form, which is then readily converted to fatty acid salts, such as the oleate or naphthenate. The acidiiied cobalt material may be treated at elevated temperatures with olen to be converted, containing in solution oleic acid, thereafter adding aqueous caustic, heating and, after settling, withdrawing the sodium acetatecontaining aqueous layer. Also, acidification of the precipitated cobalt may be effected directly with the oleic acid.

The technique set forth above, though quite effective in recovering cobalt, involves handling of solids, which is generally less efficient than where liquid products are handled, particularly in operations involving solids recovery and transfer. Also, as a result of the alkaline oxidation, there is the possibility that some of the cobalt may be converted to the cobaltic rather than to the cobaltous state. This latter possibility could constitute a serious problem, for conversion of cobaltic hydroxide to watersoluble forms of cobalt requires strong acids and elevated temperatures. Mere acidiiication is not sufficient to dissolve cobaltic hydroxide.

lt has now been found that if the cobalt solution from the acid decobalter which solution contains cobalt both in the anionic and cationic forms, is added to an aqueous solution of a fatty acid salt such that the pH of the mixture is in the range of about 5-6, i. e., on the acidic side, and the mixture is oxidized with air or oxygen at a temperature preferably in the range of about 10D-150 F., substantially quantitative recovery of cobalt is realized without the necessity of resorting to solids recovery procedures and without the danger of over-oxidation to cobaltic compounds.

The fatty acid salts may be any of those which yield cobalt salts possessing sufficient solubility in the olefinic hydrocarbon feeds to warrant use as Oxo catalysts. Such fatty acids include oleic, stearic, naphthenic, etc. A novel group of fatty acid salts which are particularly well suited to preparation of the Oxo catalysts consist of those obtained by subjecting the process bottoms to treatment with solid caustic at elevated temperatures. This type of caustic treatment produces fatty acid salts from the heavier alcohol and ester components of the bottoms The actual concentration of the sodium salts in the aqueous phase is generally aboutv 10% and the ratio of salts to decobalter extract is as required to provide approximately a stoichiometric quantity' of cobalt.

By carrying out the oxidation treatment at a pH of 5-6 certain undesirable features of previously described processes are eliminated. At pH values much above 7 insoluble forms of cobalt are precipitated and it is well known that oxidation of cobaltous compounds in alkaline solu- Vagarran'a tion can lead to formation of cobaltic compounds. The latter are not amenable to solution except at elevated temperatures and in the presence of strong acids. At pH values appreciably below 5, the oxidation proceeds very rapidly and selectively but such conditions would require use of alloy steel or glass lined equipment to eliminate serious corrosion problems. If these are available oxidation may be carried out at any acid concentration below a pH of 7. However, the pH range of 5-6 will allow use of conventional equipment and at the same time provide a rapid and selective oxidation without formation of insoluble cobalt compounds and without appreciable oxidation to the cobaltic state.

The present invention will best be understood from the more detailed description hereafter, wherein reference will be made to the accompanying drawing, which is a schematic representation of a system suitable for carrying out a preferred embodiment of the invention.

Turning now to the drawing, there is depicted merely the decobalting system as well as the conversion system of the invention. The aldehyde synthesis stage is well known at this stage in the art, and is conventional, being operated at about 200G-4500 p. s. i. g. and at temperatures of from about Z50-400 F., an oleiinic compound, about equivalent quantities of H2 and CO, and some form of cobalt, preferably oil-soluble, being fed to the primary stage.

A stream of primary stage aldehyde product containing dissolved therein relatively large amounts of cobalt carbonyl and other forms of cobalt, to the extent of about 2000 parts per million and more, is passed through line 2 to mixer 4. This unit is of any conventional design, and

is adapted to mix thoroughly an aqueous and a Water-insoluble liquid organic phase. An aqueous organic acid solution whose cobalt salts are Water soluble is injected through lines 6 and 8 into the mixer. Suitable acids are acetic, formic, propionic, and the like. Acetic acid is particularly suitable, for its cobalt salts have a relatively greater water solubility than, for instance, those of formic acid, and so less water is required for their complete recovery.l Acid is added in amounts suliicient at least to combine with all cobalt present, and the water dilution is adequate at least to dissolve all Water-soluble cobalt salts and complexes formed. Thus, a satisfactory operation may be had employing about 5-20% by Volume of a 5% aqueous solution of acetic acid. For less water soluble cobalt salts, a greater amount of water is required.

The temperature in mixer 4 must not exceed about 200 F., and is preferably about 15G-185 F., to prevent thermal instead of chemical decomposition of cobalt carbonyl into the metal.

After suiicient mixing and recirculation, on the order of 30-120 minutes, the mixture is pumped through line 10 to settler 12, where the aqueous and aldehyde layers are allowed to stratify. Substantially all of the cobalt is in the lower aqueous layer. The aldehyde layer may then be passed to water washing equipment 16 via line 14, where hot waterat about 165 F. may be injected through line 18 to Wash out the last traces of cobalt. The wash Water may, in part, be cycled to mixer 2 through line 22 as a diluent for the acid stream.

Overhead from Washing equipment 16 there is withdrawn through line 20 substantially completely decobalted aldehyde product, which is then passed to the hydrogenation stage for conversion to alcohol ina manner known per se. The lower aqueous layer, containing in solution the cationic and anionic forms of cobalt, as well as some free acetic acid, is withdrawn through line 24 and is pumped to agitator 26.

A solution of a fatty acid salt having more than about 8 carbon atoms, such as sodium oleate, dissolved in water is introduced into agitator 26 through line 36. The ratio of salt to cobalt is adjusted so that they are present in the agitator in approximately equivalent proportions. Air is passed through the mixture for about 0.1 to 2 hours 6 through line 30 and perforated distributor 32. Temperature within the reactor is maintained at about -15 0 F. and the pH'at about 5-6. lt necessary, extraneous acid may be added through 42 to maintain the reaction mixture on the acid side.

As a result of the reaction in agitator 26, the cobalt is oxidized substantially completely to cobaltous ion which in turn reacts with the sodium carboxylate to convert the cobalt to the corresponding cobalt carboxylate i. e., cobalt oleate, which is preferentially dissolved in the oletin present. lf desirable a small amount of aldehyde or alcohol product may be added to suppress foaming and emulsitication during the oxidation. The reaction mixture is withdrawn through line 40, passed to a separate stage where the lower aqueous layer, containing dissolved sodium acetate, is withdrawn and the upper layer comprising the solution of the cobalt catalyst is passed to storage, and may be employed directly in the aldehyde synthesis operation.

The invention may be further illustrated by the following examples:

Example l This example is designed to show the presence of cobait in anion form in the solutions from decobalting with acetic acid.

10 cc. of cobalt acetate solution from acid decobalting in a commercial iso-octyl alcohol plant was introduced under 40 cc. 0.1003 N KOH and well mixed (pH=ll.0) with no air agitation. The slurry was liltered and filtrate caught in and mixed with 10 cc. fuming nitric acid and several drops of bromine. The mixture was evaporated to dryness and residue dissolved with concentrated sulfuric acid. Cobalt was determined electrolytically, and 0.0274 gm. Co was deposited.

Total Co in original sol.=0.l044 gm.

tiometric titration method and found to contain 30% cobalt as the anion.

Percent as anion= Example Il This example illustrates that cobalt is incompletely removed from aqueous solutions from acid decobalting when employing conventional methods of preparing cobalt salts of fatty acids.

A mixture of sodium soaps was prepared by treating the heavy bottoms obtained as a by-product in the commercial preparation of iso-octyl alcohol with 15% solid caustic at 500 F., for 6 hours. A Weight of 202 grams of the 4crude soaps was mixed with 1300 ml. of warm water and the pH of the mixture adjusted to about 8 by the addition of 50% sulfuric acid. This mixture was then agitated for 15 minutes with 50 ml. of a C7 polypropylene fraction and 700 ml. of a cobalt solution obtained by decobalting iso-octyl aldehyde with an aqueous solution of acetic acid. The cobalt solution contained 1.73 wt. per cent cobalt, of which 0.81% (47% of the total) was present in the form of the anion. Under these conditions the soap was present in considerable stoichiometric excess. The mixture was separated into organic and aqueous layers, the. former having a cobalt content 3.27 wt. per cent and representing 49% of the cobalt originally added. The aqueous layer was analyzed by potentiometric titration and found to contain 0.41 wt. per cent cobalt'of which 0.36% (or 88% of the total cobalt) was present as the anion. Within the accuracy of the analysis, the recovery of cobalt in the form of the anion in the water layer was 100% of that added as the anion.

Example III lt has been found that if the cobalt solution is added to an aqueous solution of a fatty acid salt such that the Total acid, wt. per cent as HAc 1.42 Cobalt, wt. per cent as Co++ 0.92 Cobalt, wt. per cent as Co(Co4)- 0.81 (47% of total) The soaps used in these preparations were obtained by treating oxo (fractionator) bottoms with caustic at 500 F., for 6 hours. The amount of soaps indicated were dissolved in 800-1300 ml. of water and treated under the conditions indicated.

2. In a carbonylation process wherein olenic carbon compounds are contacted in a carbonylation zone with CO and Hz in the presence of a cobalt catalyst under conditions including temperatures of from about 150 to 450 F. and pressures of from about 1500 to 4500 p. s. i. g. to produce reaction products comprising aldehydes containing at least one more carbon atom than said olenic compounds, and wherein a solution comprising said reaction products and dissolved cobalt catalyst is transferred to a catalyst removal zone and said cobalt is recovered, the improvement which comprises contacting said cobalt-contaminated aldehyde product with an aqueous solution of an organic acid at a temperature of from about 150 to about 200 F., converting said cobalt compounds into water-soluble forms of cobalt, withdrawing from said zone an aqueous solution contain- RunNo 7 8 Percent. Percent of Cobalt Recovered in Catalyst Solution.4 Analysis of aqueous layer:

Total cobalt, wt. percent Anlouic cobalt, wt. percent Percent recovery of anionic cobalt in aqueous layer.

Aldehyde. .51

Yes.

C1+ Decobalted Aldehyde.

1 Soaps initially mixed with 1300 ml. water. pH adjusted to 7-8 by addition of H2804. 2 Soaps initially mixed with 830 m1. water. pH adjusted to 7-8 by addition of HiSOi. 3 Air blown for 15 minutes at indicated temperatures and pH in the range of 5-6.

4 Based on total cobalt present in acid decobalter solution.

These data illustrate very clearly the effects of increased temper-ature and air blowing on the cobalt recovery in the catalyst solution. Runv No. 9 which is representative of air blowing at 13G-.140 F. gave essentially complete recovery of cobalt.

What is claimed is:

1. ln a carbonylation process wherein olenic carbon compounds are contacted in a carbonylation zone with CO and H2 in the presence of a cobalt catalyst under conditions including temperatures of from about 150 to 450 F. and pressures of from about 1500 to 4500 p. s. i. g. to produce reaction products comprising aldehydes containing at least one more carbon atom than said oletinic compounds, and wherein a solution cornprising said reaction products and dissolved cobalt catalyst is transferred to a catalyst removal zone and said cobalt is recovered, an improved method of removing and recovering said cobalt from said aldehyde product which comprises contacting said cobalt-contaminated aldehyde product with an aqueous solution of an organic acid at a temperature in the range of about 150 to about 200 F., converting said cobalt compounds dissolved in said aldehyde into water-soluble forms of cobalt, passing aldehyde product and aqueous solution of cobalt to a settling zone, withdrawing a substantially cobalt-free aldehyde product from said zone, withdrawing from said zone an aqueous solution of cobalt compounds wherein cobalt is present both in an anionic and a cationic form, passing said solution to a treating zone, making said solution acidic in said treating zone, subjecting said aqueous solution made acidic to an oxidizing treatment at about 100 to 150 F. whereby cobalt is converted substantially into cobaltous ion, and converting cobaltous ion-containing solution into oleiin-soluble cobalt salts.

ing anionic and cationic forms of cobalt, subjecting said solution to an oxidation reaction in the presence of a compound of an alkali metal and free acid giving the solution a pH of about 5 to 6, and recovering substantially completely said cobalt as a cobalt soap.

3. The process of claim 2 wherein said solution is subjected to said oxidation treatment in the presence of a sodium salt of a relatively high molecular weight fatty acid as said compound of an alkali metal.

4. The process of claim 3 wherein said salt is sodium oleate.

5. Theprocess of claim 3 wherein said salt is sodium naphthenate.

6. The process of claim 3 wherein said salt is the reaction product obtained by treating oxo bottoms with caustic at elevated temperatures.

7. The process of claim 2 wherein said oxidation is carried out by air blowing at about 10U-150 F.

8. The process of claim 2 wherein said recovered cobalt soap is employed to catalyze the aldehyde synthesis reaction.

9. The process of claim 3 wherein said treatment is carried out in the further presence of an olen.

References Cited in the tile of this patent UNITED STATES PATENTS 2,547,178 Spence Apr. 3, 1951 2,638,487 Russum et al. May 12, 1953 FOREIGN PATENTS 679,664 Great Britain Sept. 24, 1952 

1. IN A CARBONYLATION PROCESS WHEREIN OLEFINIC CARBON COMPOUNDS ARE CONTACTED IN A CARBONYLATION ZONE WITH CO AND H2 IN THE PRESENCE OF A COBALT CATALYST UNDER CONDITIONS INCLUDING TEMPERATURES OF FROM ABOUT 150 TO 450* F. AND PRESSURES OF FROM ABOUT 1500 TO 4500 P.S.I.G. TO PRODUCE REACTION PRODUCTS COMPRISING ALDEHYDES CONTAINING AT LEAST ONE MORE CARBON ATOM THAN SAID OLEFINIC COMPOUNDS, AND WHEREIN A SOLUTION COMPRISING SAID REACTION PRODUCTS AND DISSOLVED COBALT CATALYST IS TRANSFERRED TO A CATALYST REMOVAL ZONE AND SAID COBALT IS RECOVERED, AN IMPROVED METHOD OF REMOVING AND RECOVERING SAID COBALT FROM SAID ALDEHYDE PRODUCT WHICH COMPRISES CONTACTING SAID COBALT-CONTAMINATED ALDEHYDE PRODUCT WITH AN AQUEOUS SOLUTION OF AN ORGANIC ACID AT A TEMPERATURE IN THE RANGE OF ABOUT 150 TO ABOUT 200* F., CONVERTING SAID COBALT COMPOUNDS DISSOLVED IN SAID ALDEHYDE INTO WATER-SOLUBLE FORMS OF COBALT, PASSING ALDEHYDE PRODUCT AND AQUEOUS SOLUTION OF COBALT TO A SETTLING ZONE, WITHDRAWING A SUBSTANTIALLY COBALT-FREE ALDEHYDE PRODUCT FROM SAID ZONE, WITHDRAWING FROM SAID ZONE AN AQUEOUS SOLUTION OF COBALT COMPOUNDS WHEREIN COBALT IS PRESENT BOTH IN AN ANIONIC AND A CATIONIC FORM, PASSING SAID SOLUTION TO A TREATING ZONE, MAKING SAID SOLUTION ACIDIC IN SAID TREATING ZONE, SUBJECTING SAID AQUEOUS SOLUTION MADE ACIDIC TO AN OXIDIZING TREATMENT AT ABOUT 100* TO 150* F. WHEREBY COBALT IS CONVERTED SUBSTANTIALLY INTO COBALTOUS ION, AND CONVERTING COBALTOUS ION-CONTAINING SOLUTION INTO OLEFIN-SOLUBLE COBALT SALTS. 